Motor-control system



Nov. 24, 1925. 1,562,968

' B. W. JONES MOTOR CONTROL SYSTEM Filed May 6. 1924 Fig.2.

' InJefitow: Ber iamin \MJoneS,

M TA

His Attorney.

Patented Nov. 24, 1925.

UNITED STATES 1,562,968 PATENT OFFICE.

BENJAMIN W. J ONES, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAIl ELEG-TRIC COMPANY, A CORPORATION OF NEW YORK.

MOTOR-CONTROL SYSTEM.

Application filed May 6, 1924. Serial No 711,494.

T all whom it may concern:

.Be it known that I, BENJAMIN WV. JoNEs,

a citizen of the United. States, residing at Schenectady, in the countyof Schenectady, 8 State of New York, have invented certain new anduseful Improvements in Motor- Control Systems, of which the following isa specification.

My invention relates to systems of control 10 means whereby the motorsare started and smoothly accelerated under Widely varying serviceconditions.

One of the objects of the invention is to provide an improvedarrangement whereby the motor is controlled in response to the rate ofchange of an operating condition, such, for example, as the rate ofchange of the motor speed or the rate of change of an electricalcharacteristic of the motor or the motor circuits which is responsive tothe rate of change of the speed of the motor.

Although the invention is not necessarily limited thereto, it has aparticular application in systems of direct current motor controlwherein the control of the motor is effected by means of resistance inseries with the motor armature and other resistance arranged to beconnected in shunt to the motor 30 armature. A common form of controlhaving resistance in series with the motor armature and anotherresistance in shunt thereto employs switch mechanism for controlling theresistance so arranged that sections of the 35 resistance arealternately included in shunt to the motor armature as sections of theresistance in series with the motor armature are short-circuited duringthe acceleration of the motor. A common arrangement of this sort is onein which double throw electromagnetic switches or contactors areprovided, each switch arranged to normally short-circuit a section ofshunt resistance and when energized to remove the shortcircuit about thesection of shunt resistance and short-circuit a section of the seriesresistance. Thus, a. section of the resistance is cut into the shuntcircuit about the motor armature substantially simultaneously withcutting out a section of the resistance in series with the motorarmature. Arrangements of this sort are objectionable because of theinflexibility thereof. Thus, in case the control system is employed forgoverning an electric motor driving an for electric motors and itprovides improved elevator, hoist or the like, if the operator does notuse care and intelligence in the manipulation of the master switchcontrolling the electromagnetic resistance switches, he is apt to effecta too rapid operation oi the resistance switches. If the operatormanipulates the master switch so as to start the elevator moving downwith a heavy load on the elevator and moves the master switch from theoff position towards the maximum speed down position very slowly, theelectromagnetic switches would alternately vary the shunt and the seriesresistances with sufiicient interval between the one step of the controlto the next, so that the elevator is accelerated smoothly and gradually.However, if the operator turns the controller rapidly from the OK to themaximum speed down position, a very high accelerating torque is appliedto the motor, in addition to the high over-hauling load torque and thiscauses a very rap-id acceleration of the elevator which'isobjectionable. In accordance with my invention, I provide a flexibilitybetween the successive steps of including a. resistance in shunt to themotor armature and short-circuiting a resistance in series with themotor armature, so that at least one of the resistances will be governednot only in response to the prior operation of varying the otherresistance but also in response to the rate of change of an operatingcondition of the motor or the motor circuit, such for example as therate of change of the counter electromotive force of the motor.

In accordance with the invention in the form which I now regard as thepreferred form, if the operator manipulates the master controller veryquickly, the short circuiting of the series resistance will notimmediately follow the inclusion of resistance in shunt to the motorarmature, as in prior arrangements, but will be delayed depending uponthe rate of change of the counter electromotive force of the motor, soas to thereby permit the motor to accelerate smoothly and automaticallyprevent increasing the accelerating torque too rapidly. If the op eratormanipulates the master controller slowly, the operation of the equipmentwill be substantially the same as the said prior arrangement, namely,the series resistance will be out out substantially simultaneously withthe cutting in of the resistance in shunt to the motor armature. If theload is to be hoisted, the rate of change controlling devices connectedand arranged in accordance with the invention will permit the seriesresistance to be short-circuited step by step p in a more rapid sequencethan in the ease of starting the elevator down with a heavy over-haulingload, and the motor-is thereby forced to accelerate its'load at thecorrect rate. In other words, the control in accordance with theinvention automatically takes care of such varying conditions as thevariations of the speed of operation of the master controller, thevariations in the value of the load on the elevator, as to whether ornot the load is being hoisted or lowered, and as to whether or not theload is over-hauling or otherwise.

For a better understanding of my invention, reference is had to thefollowing description taken inconnection with the V accompanying drawingin which Fig. 1 is a sim lified diagram illustrating a motor controsystem embodying my invention for the purpose of explaining theprinciples thereof, and Fig. 2 diagrammatically illustrates a reversingmotor control system suitable for elevator service, likewise embodyingthe invention.

The novel features which I believe to be characteristic of my inventionare set forth with articularity in the appended claims. Re erring firstto Fig. 1 of the drawing, the motor 10 which is controlled according tomy invention is shown as of the direct current type having an armature11 and a shunt field winding 12. The resistances 13 and 14 are connectedrespectively in series and in shunt with the armature 11 and are ofsuitable ohmic value to limit the motor to a desired low speed when thenormally open electro-magnetic line switch 15 is closed to connect themotor 10 to a suitable source of supply. The normally closedelectromagnetic switch 16 is connected in circuit with the shuntresistance 14 and is operable to the open position to interrupt thecircuit through the resistor 14. The manually operable master controller17 is provided for controlling the energizing circuits of theelectromagnetic switches 15 and 16;

In order to control the series resistance- 13 in-accordance with therate of. change of the motor speed efl'ected by operation of the mastercontroller 17, I provide the electroresponsive switch mechanism 18. Inthe preferred form shown, this electroresponsive switch mechanism is ofthe general type described and broadl claimed in my copending aplication or patent, Serial No. 595,875, fi ed October 20, 1922. ,Itwill be observed that this type of switch mechanism is provided with anenergizing winding 19 and a short-circuited winding 20 which arearranged to cooperate in controlling the actuation of the pivotedcontact member 21.. While this particular type of electroresponsiveswitch is well adapted for use in my resent invention I would have itunderstood that the present invention is not limited thereto since othertypes of electroresponsive switches may be employed if desired.

With-the arts in their respective osi tions shown in Fig. 1 theoperation 0 my improved control system is as follows: Upon operating themaster controller 17 to the first position, the winding of line switch15 is energized and the switch'operates from the open position shown tothe closedposition and connects the motor 10 to a suitable source ofsupply. As previously pointed out the series resistance 13 and the shuntresistance 14 limit thespeed of the motor 10 to a low value dependingupon the relative ohmic values of the resistances 13 and 14, as well asthe value of the load driven by the motor 10. Upon the further operationof master controller 17 to the second position, the electroma eticswitch 16 is energized to open the s unt circuit around the motorarmature 11 including the resistance 14. The resulting increase ofcurrent through the motor armature increases the motor tor ac and tendsto accelerate the motor to a igher speed. Upon the opening its motiveforce correspondingly increases in value. Due to the inductive relationbetween the energizing winding 19 and theshort circuited winding 20, thelatter is thereupon energized res'ponsively to the rate of change of themotor counter electromotive short circuited winding 20 is below thepredetermined value. v

Should the motor be heavily loaded so as to accelerate slowly uponopening of the switch 16, the short circuited winding 20 will not beenergized sufficiently to prevent the pivoted switch member 21' frombeing operated to the closed osition by the energizing winding 19. Un erthese conditions the short circuits the series resistance 13, therebyfurther'increasing the motor torque to 'hasten the response of the motor10 to the operation of master controller 17.

If, however, the motor is lightly loaded so as to be rapidly acceleratedupon the opening of the manually controlled switch 16, theelectroresponsive switch mechanism 18, then functions to delay theclosing of the short circuit around the series resistance 13, while therate of change of the motor speed and consequently the rate of change ofits counter electromotive force is above a predetermined value. In thiscase, upon the opening of switch 16, and the resulting energization ofthe winding 19 responsively to the motor counter electromotive force,the short-circuited winding 20 is strongly energized and prevents theoperation of the pivoted contact member 21 to the closed position by theenergizing 'winding 19. After the acceleration of motor 10 has reached asubstantially constant value determined by the value of the seriesresistance 13, and the rate of change of the motor counter electromotiveforce is below a predetermined value, the inductive energization ofshort circuited winding 20 is reduced to a value which permits thepivoted contact 21 to close and short circuit the series resistance 13.Thereupon the motor 10 is accelerated to full running speed.

Referring now to the reversing motor control system shown in Figure 2 ofthe drawing, it will be understood that for elevator service thearmature 11 of the motor 10 is mechanically connected by means not shownin the drawing to drive an elevator car or other hoisting apparatus. Theelectromagnetic reversing switches 23 and 24, together with theelectromagnetic line switch 25 are provided for connecting the motor 10to the supply lines 26 and 27 for operation in either direction. Inorder to operate the motor 10 at a plurality of definite speeds with anoverhauling load as well as an underhauling load the severalresistances, 28, 29, 30, and 31 are connected in a shunt circuit acrossthe motor armature 11, and

the resistances 32, 33, 34, 35, and 36 are connected in series with themotor armature 11. The shunt resistances 28, 29, 30 and 31 arecontrolled respectively by the normally closed electromagnetic switches37, 38, 39 and 40 and these electromagnetic switches are arranged to beoperated in a predetermined sequence under the control of the manuallyoperated master switch 41 which also controls the energizing circuits ofthe electromagnetic reversing switches 23 and 24 and the electromagneticline switch 25.

To automatically control the rate of change of the motor speed which maybe effected by operation of the manually controlled master switch 41,the electroresponsive switch mechanism comprising in the preferred formshown the relays 42 and 43, each having an energizing winding 44 and 45and a short circuited winding 46 and 47 respectively together with thenormally opened electromagnetic switches 48, 49, 50,

51, and 52 which are provided for controlling the series resistances 32,33, 34', 35 and 36 in a manner which best will be understood from thefollowing description of the operation of the control system shown inFig. 2. Each of the relays 42 and 43 is similar in design andconstruction to the electromagnetic switch 18 shown and described inconnection with Fig. 1 and the short circuited windings 46 and 47 are ininductive relation with the energizing windings 44 and 45 respectively.It will be observed that the energizing winding 44 of the relay 42 isconnected to the auxiliary contact 53 which is engaged upon theoperation of the electromagnetic switch 37 to the open position and theenergizing winding 45 of the relay 43 is also connected to acorresponding auxiliary contact 54 on the electromagnetic switch 39.

With the se eral parts thus constructed and arranged the operation ofthe control system shown in Fig. 2 is as follows: Assuming the supplylines 26 and 27 are connected to a suitable source, the motor 10 may beoperated in the hoisting direction by moving the master controller 41progressively to the positions indicated as 1, 2, 3, 4, 5, and 6 in thedrawing. In position 1, an energizing circuit for the reversing switch23 is completed from the supply line 26 through the contact segments 61and 62 of master controller 41, the conductor 63, the operating windingof the electromagnetic switch 23 and the conductor 64 to the othersupply line 27 and switch 23 is operated from the open position, towhich it is biasedas shown, to the closed position and establishesconnections for operating the motor 10 in the desired direction uponclosure of line switch 25. In the second position of the mastercontroller, a circuit is closed from the supply line 26 through thecontact segments 61 and 66 of the master controller 41, the conductor 67the operating winding of the electromagnetic line switch 25 and theconductor 68 to the other supply line 27. Upon the resulting closure ofline switch 25, the motor armature 11 is con nected in series with theresistances 32, 33, 34, 35 and 36 to the supply line 26 and 27 with theresistance 28 connected in shunt with the motor armature 11 through thenormally closed electromagnetic switch 37 the other shunt resistances29, 30 and 31 being short circuited at starting. As the mastercontroller 41 is moved into the third position an energizing circuit forthe'operating winding of the electromagnetic switch 37 is completed fromsupply line 26 through the contact segments 61 and 69, the conductor 70,the operating winding of switch 37 and the conductor 68 to the othersupply line 27. Thereu on the electromagnetic switch 37 'respon s toopen the shunt circuit through .the resistance 28 and to connect theenergizing winding 44 of the remotor counter electromotive force toprevent closure of the relay contact when the motor accelerates rapidlydue to the opening of switch 37. In either case the relay 42 closesitscontact when the rate of change of the motor speed-is below apredetermined value and thus establishes an energizing circuit for theoperating winding of electromagnetic switch 48 from: the supply line 27,through the contacts of relay 42, the winding of switch 48, and thecon.-

-ductor 71 to the other supply line 26.

Closure of switch 48 establishes a short circuit around theresistance.32, thus further accelerating the motor 10.

Upon closure of electromagnetic switch 37 an energizing circuit for' theelectromagnetic switch 38 is established through the auxiliaryinterlocking contact 72 with which electromagnetic switch 37 isprovided. Hence upon operation of the master controller 41 to the fourthposition, the operating winding of switch 38 is energized through thecontact segment 73, the conducfor 74, the auxiliary contact 72, theoperating winding of electromagnetic switch 38' and the conductor 68 tothe other supply line 27. Switch 38 thereupon operates to open the shuntcircuit through the resistance 29 and thereby again increases the speedof motor 10. In a similar manner the electromagnetic switch 39 isenergized through the auxiliary contact of electroma netic switch 38 andthe contact segment 6 of master controller 41 when the latter is operated to the fifth position andopens the shunt circuit throughthe'resistance 30 and accelerates the motor 10 "to a higher speed.Opening of the switch 39 connects the energizing winding 45 of theelectromagnetic relay 43 across the motor armature 11 and the shortcircuited winding 47' either permits the immediate response of the relaywhen the rate of change of motor counter electromotive force is below apredetermined value or delays the response of'the relay 43 in case themotorcounter electromotwe force is lncreasmg at a rate above thepredetermined value, in exactly the same manner as was described inconnection with the relay 37 Upon the response of relay 43 the switch 49is energized through a circuit including the auxiliary contact83 ofswitch 48 and operates to. short circuit the resistance 33. The motorthen may be accelerated to full running speed by operation of the mastercontroller 41 to the sixth osition.- This effects the ener i'zation of te electromag netic switch 40 t rough the contact segment 78 of themaster controller and the auxiliary contact 79 on switch 39, and switch.40 o erates from the closed position to open t e entire shunt circuitacross the motor armature including the resistances 28, 29, 30 and 31.The auxiliary contact 80 with .which the electromagnetic switch 40 isprovided completes the energizing circuit for 'the operat ng winding ofelectromagnetic .switch 50 which may be traced from the supply line 27through the auxiliary contact 81 on electromagnetic switch 49, auxiliarycontact 80 on switch 40, the winding .of electromagnetic switch 50 andthrough the conductor 71 to the other supply line 26. The successiveoperation of the electromagnetic switches 50, 51 and 52, to shortcircuit the 'series'resistances 34, 35 and 36 respectively thereuponoccurs in an obvious manner since the successive energization of eachswitch is controlled by an interlocking contact which is closed uponoperation of the preceding switch.

U on the return of the master controller 32 through the successivepositions 6, 5, 4, 3 and 2, the resistance controlling switches :areprogressively deenergized and returned to their respective positionsshown thus again inserting the series and shunt resistances in circuitwith the motor armature to decelerate the motor through a sequence ofdefinite speeds, to its lowest operating speed.

Further movement of the master controller 41 through the position 1 tothe off position shown interrupts the energization of line switch 25 andreversing switch 23 and brings the motor to a stop.

In order to operate the motor 10in the reverse or lowering direction,master controller 41 is operated to engage the right hand set of contactsegments. In this case the electromagnetic reversing switch 24 is firstenergized through the contact segment 82 and the line switch 25 and theseveral resistance controlling electromagnetic switches are successivelyoperated in exactly the same manner as previously described toaccelerate the motor through a series of intermediate s eeds.

It should e notedthat if during the acceleration of the motor 10 ineither direction as reviously described, the load on the motor s iouldbe such that the rate of acceleration after the -o eration of either themanually controlle electromagnetic switch 37 or 39, is below the valueat which the short circuited winding 46 and 47 of the electromagneticrelays 42 and 43 res ectively are operatively energized, each 0 therelays immediately responds to efiect the short circuiting of thecorresponding series resistances 32 and 33 to accelerate the rate ofchange of motor 10 produced by the closing of the electromagneticswitches 28 and 30 res ectively.

If, owever, an impetuous or careless operator should throw the mastercontroller 41 from the off position to the full speed running positionso that themotor is connected to the source of supply and the manuallycontrolled electromagnet switches 37, 38, 39 and 40 are operated inrapid succession to accelerate the motor at a correspondingly rapidrate, each of the electromagnet relays 42 and 43 then operates toprevent the short circuiting of series resistances 32, 3'3, 34, 35 and36 in the following manner. Upon the operation of the electromagneticswitch 37 to connect the energizing winding 44 of relay 42, across themotor armature, the short circuited winding 46 is thereupon inductivelyenergized responsively to the rate of change of the motor counterelectromotive force, as previously described. Hence, while the motor isaccelerating due to the successive operation of the electromagneticswitches 38, 39 and 40, the short circuited winding 46 prevents theresponse of relay 42 and the consequent energization of theelectromagnetic switch 48 to short circuit the series resistance 32. Therelay 43 likewise is prevented from closing upon the operation ofelectromagnetic switch 39 by the short circuit winding 47.

Thus it will be seen that the series resistances 32, 33, 34, 35 and 36are maintained in circuit with the motor armature and serve to preventan unduly rapid response of the motor 10 to an improper operation of themaster controller 32 such as assumed above.

When the rate of acceleration of motor 10 falls below at predeterminedvalue, the short circuited winding 46 of relay 42 will not be energizedsufiiciently to prevent closure of the relay contacts by the energizingwinding 44 and the relay 42 thereupon responds to energize theelectromagnetic switch 48 which operates to short circuit the resistance32. After the motor 10 has again accelerated and reached a substantiallyconstant speed, the short circuited winding 47 of relay 43 will bedeenergized and permit the closing of relay 43, electromagnetic switch49, 50, 51 and 52 in the regular order previously described.

It will be evident to. those skilled in the art that suitable limitswitch mechanism as well as overload safety switch mechanism may beprovided for protecting the motor 10 if desired.

In accordance with the provisions of patent statutes, I have describedthe rinciple of operation of my invention, toget or with the apparatuswhich I now consider to represent the best embodiment hereof, but Iwould have it understood that the invention may be carried out by othermeans.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,-

1. In a motor control system, the combination of an electric motor, aresistance arranged to be connected in shunt to the motor armature, aresistance in series with the motor armature, a plurality ofelectroresponsive switches normally operable in a predetermined sequencefor varying the said resistances to change the motor speed, and meansoperated responsively to the rate of change of the motor speed forpreventing the operation of a portion of the said switches to vary oneof said resistances when the change in the -motor speed exceeds apredetermined value upon the operation of another portion of saidswitches to vary the other of said resistances.

2. In a motor control system, the combination of an electric motor, aresistance arranged to be connected in shunt with the motor armature, aresistance in series with the motor armature, a plurality ofelectroresponsive switches for varying the said resistances, manuallyoperated means for controlling the connection of the motor to a sourceof supply and for operating a portion of said switches to vary the saidshunt resistance and thereby accelerate the motor, and means operatedresponsively to the rate of change of the motor speed for operatinganother portion of said switches to vary the said series resistance toaccelerate the motor when the rate of change of the motor speed due tooperation of the said first portion of the switches is below apredetermined value.

3. In a motor control system, the combination with the motor, of aplurality of resistances, one connected in shunt and another in serieswith the motor armature,

"switch mechanism for varying one of the said resistances to change themotor speed, an electromagnetic switch for controlling the other of thesaid resistances to change the motor speed, electric connectionsestablished upon the operation of said first switch mechanism forenergizing a winding of said electrom etic switch responsively toanelectrical iiharacteristic of the motor which varies with the speedthereof, and means arranged to prevent response of said electroi cludinan electromagnetic switch controlled by sai first switch mechanism andhaving a winding energized responsively' to the rate of change of themotor which varies with the speed of the motor, and a second windinginductively related with said first winding to prevent operation of theswitch to short circuit said series resistance while the rate of changein said electrical characteristic is above a predetermined value.

5. In a motor control system, the combination with the motor, of aplurality of resistances, one connected in shunt and another in serieswith the motor armatures, switch mechanism operable between twopositions for controlling one of said resistances, and anelectromagnetically actuated switch for controlling another of saidresistances and havin an operating winding energized responsive y to thecounter electromotive force of the motor upon operation of said firstswitch mechanism to one position and a short circuited windinginductively energized from said first winding for delaying operation ofthe switch while the rate of c ange of the motor counter electromotiveforce is above a predetermined value.

6. In acontrol system, the combination of an electric motor, a pluralityof resistances connected in circuit with the motor for controlling thespeed thereof, one of said resistances being connected in shunt with themotor armature and another of said resistances being connected in serieswith the motor armaan electrical characteristic of v open position anture, switch mechanism for connecting the motor to a source of sup lyfor o ration thereof and for varying said unt re sistan' ce toacceleratethiei motor;i a havanen win ngan aso cirb u ted wiiib iifg anelectromagnetic switch biased to the open position and having anoperating wind-mg controlled. by said relay for establishing a shortcircuit around the said series resistance, and electrical connectionscontrolled by said switch mechanism for connecting the energizingwinding of said relay across the motor armature w e by the said shortcircuited windin is energized responsively to the rate of c ange in thecounter electromotive force of the motor to prevent the short circuitingof said series resistance while the rate of acceleration of the motor isabove a predetermined value. 7. In a control system, the combination ofan electric motor, a plurality of resistances, one connected in shuntand another in series with the motor armature, an electromagnetic switchconnected" in circuit with said shunt resistance and biased to theclosed position, a second electroma netic switch biased to the operableto the closed position to establish a short circuit around the saidseries resistance, a master switch for connecting the motor to a sourceof supply and for controlling the operation of. said firstelectromagnetic switch, a relay for controlling the energizing circuitof said second electromagnetic switch, said relay having an energizingwinding and a short circuited winding, and electrical connectionswhereby when the said first electromagnetic switch is operated to theopen position, the said energizing winding of said relay is connectedacross the motor armature and the said short circuited winding isenergized responsively to the rate of change in the counterelectromotive force of the motor to prevent the energization of saidsecond electromagnetic switch when the rate of acceleration of the motoris above a predetermined value. a a v In witness whereof, xI havehereunto set my hand this 5th day of May, 1924.

BENJAMIN w. JONES..

